<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
//    var reg = /http:\/\/.*?"/g;
//xxsx@sina.com.cn
    var reg = /^[0-9a-z_][0-9a-z_\.]*?@[0-9a-z]+(\.[a-z]{2,5}){1,2}$/i;
    var s = 'frank.chan.chan@qq.com.cn';

    var r = s.match(reg);
    console.log(r);
</script>
</body>
</html>